1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a wide mount polyethylene terephythalate (PET) container and a method for making the same.
2. Description of the Related Art
Wide mouth bottles having threaded necks typically have neck finishes larger than 48 mm in diameter, and the majority of those bottles are produced on single stage injection mold equipment. This equipment is well suited for low volume applications primarily because the slower injection process is the determining factor in cycle time. For high volume applications two-stage PET equipment has been developed to make preforms having the desired finished threaded neck configuration in a separate injection molding machine and then reheating and blowing the preforms in another blowing machine. FIG. 5 shows a preform having the finished thread finished superimposed on a bottle produced using the preform. However, in this arrangement the blowing machine can out-produce the injection machine and preform inventories must be carefully monitored to keep an adequate supply for the blowing machine. This imbalance is compounded when two-stage equipment is used in wide mouth applications. This is primarily due to the size of the preform/neck finish and the physical size of the injection mold.
The single stage blow molding process combines the injection of the preform and blowing of the container into one machine. These machines have an extruder that melts the resin pellets and injects the molten resin into a mold to form the preform. The preform is then transferred to a conditioning station that either adds or removes heat from areas of the preform to help with forming the container. In some machines such as an Aoki, the conditioning station is eliminated and the preform design is the only factor used to determine material placement in the container. After the conditioning station, the preform is transferred to the blow station where the container is formed. The last operation is removing the container from the machine. This can be done in a fourth station as in a Nissei and Sipa or directly from the blow station as in Uniloy USB machines. In all one stage machines, the injection time determines the overall cycle time.
The size of the injection platen (preform neck diameter) and blow mold platen determine the maximum container size. On containers with small finishes (preform neck diameter), the container diameter determines how many will fit on the blow platen. Once the finish becomes large enough, the number of cavities is determined by how many preforms will fit into the injection station. Usually, more containers of a given body diameter can be produced if the finish diameter is reduced. By using the Trim-Lite process on a single stage machine, the finish size is kept small enough to allow the container diameter to determine the maximum number that can be produced in a single cycle.
In other words, although wide mouth PET containers can be manufactured on single stage PET blow molding machine, the number of mold cavities possible is wholly dependent on the diameter of the neck finish of the preform.
For example, when running a 155 mm diameter canister, the maximum cavitation on the existing machinery was limited to 2 (this represents the number of units that may be blow molded at one time). Note the large diameter of the threaded portion of the typical preform as shown in FIG. 5. Secondly, the neck (as with all single stage injected molded preforms) would have been solid plastic and would contribute a large portion to the overall bottle weight.
The finish diameter also affects the design of the preform and the material distribution in the blown container. As the finish diameter increased, the preform takes on a flatter, disc like shape resulting in less desirable stretching characteristics. A smaller finish allows the preform design to be more cylindrical which provides for better stretching characteristics.
Notably, when using the one stage blow molding process, the heat from the injection process is maintained in the preform. Thus, the preform is not cooled into a solid state. This means that the one stage preform is generally heated throughout more than the two stage preform prior to blowing. Because of the one stage preform having more internal heat, it can form small details better than the two stage process. The two stage process on the other hand due to it having less internal heat develops more stress hardening of the material and produces a stronger container for a given design. However, because the neck finish of wide mount containers is large, the number of mold cavities in the one stage blow molding machine is limited due to the available space. Thus, there is a need to for an improved method for making wide mouth PET containers.